1. Field of the Invention
The present invention relates to a method and an apparatus to control a disk drive, and more particularly, to a method and apparatus directed to acceleration-based track seeking servo control of a disk drive, to reduce noise and to shorten track-to-track seek time in the disk drive.
2. Description of the Related Art
A hard disk drive includes a plurality of magnetic transducers that write and read information by magnetizing and sensing a magnetic field of a single rotating disk or each of a plurality of rotating disks coated with a magnetic medium. The information is stored in a plurality of sectors located in an annular track. A track number is allocated across each surface of a disk, and a vertical set of tracks is called a cylinder. Thus, each track may be defined by a cylinder number.
Typically, each of the plurality of magnetic transducers is integrated into a slider incorporated into a head gimbal assembly (HGA). Each HGA is attached to an actuator arm having a voice coil located adjacent to a magnetic assembly which together defines a voice coil motor. The hard disk drive typically includes a driving circuit and a controller that supply current to excite the voice coil motor. The excited voice coil motor rotates the actuator arm and moves the transducers across the surface of disk(s).
When writing or reading information, the hard disk drive performs a seek routine to move the transducers from one cylinder to another cylinder. During the seek routine, the voice coil motor is excited by current to move the transducers to a new cylinder position across the surface of disk(s). The controller performs a servo routine to insure that the transducer follows on the center of a track.
A minimization of the amount of time required to read information from or writing information to disk(s) is desirable. Thus, the seek routine performed by the hard disk drive must move the transducers to the new cylinder position within a short time. Additionally, a settling period of the HGA must be minimized, so that the transducers can rapidly write or read information and move rapidly near the new cylinder position.
In general, seek servo control is performed by using a square wave acceleration trajectory, so as to quickly move the transducers to a target track. However, square waves include harmonics with high frequency characteristics, which causes mechanical resonance and excites mechanical elements or assemblies with high natural frequencies. Audible noise, undesired vibration, and an increase in the settling time of the HGA are caused due to residual vibration. The mechanical resonance introduced by square waves has a drawback in that both the settling time and the whole time required to write information to or read information from disk(s) are increased.
To solve such a problem, a seek control method using a sine wave acceleration trajectory has been proposed. An acceleration equation, a velocity equation, and a position equation are defined below.
                                                                                             a                  ⁡                                      (                    t                    )                                                  =                                                      K                    A                                    ⁢                                      I                    M                                    ⁢                                                                          ⁢                                      sin                    ⁡                                          (                                                                                                    2                            ⁢                                                                                                                  ⁢                            π                                                                                T                            SK                                                                          ⁢                        t                                            )                                                                                                                                                                v                  ⁡                                      (                    t                    )                                                  =                                                                                                    K                        A                                            ⁢                                              I                        M                                            ⁢                                              T                        SK                                                                                    2                      ⁢                                                                                          ⁢                      π                                                        ⁡                                      [                                          1                      -                                              cos                        ⁡                                                  (                                                                                                                    2                                ⁢                                                                                                                                  ⁢                                π                                                                                            T                                SK                                                                                      ⁢                            t                                                    )                                                                                      ]                                                                                                                                                                x                    ⁡                                          (                      t                      )                                                        =                                                                                                              K                          A                                                ⁢                                                  I                          M                                                ⁢                                                  T                          SK                                                                                            2                        ⁢                                                                                                  ⁢                        π                                                              ⁡                                          [                                              1                        -                                                                                                            T                              sK                                                                                      2                              ⁢                                                                                                                          ⁢                              π                                                                                ⁢                                                      sin                            ⁡                                                          (                                                                                                                                    2                                    ⁢                                                                                                                                                  ⁢                                    π                                                                                                        T                                    SK                                                                                                  ⁢                                t                                                            )                                                                                                                          ]                                                                      ,                                                                          (          1          )                    where coefficients KA, IM, TSK denote an acceleration coefficient, a current amplitude, a track-seek time, respectively.
In comparison with the use of the square wave acceleration trajectory, the use of the sine wave acceleration trajectory leads to an increase of the track-seek time by about 10%. Also, when the sine wave acceleration trajectory is used according to Equation 1, mechanical noise and vibration are still caused due to jerk generated at the start and end of track seeking.
Here, the jerk indicates a differential value of the acceleration (the amount of acceleration change). In particular, the jerk, generated at the start and end of track seeking, causes mechanical noise and vibration.
When the square wave acceleration trajectory is used in track seeking, the jerk is unlimited at the start and end of track seek, as indicated in Equation 2.|j(0)|=|j(TSK)|=∞  (2)
When the sine wave acceleration trajectory is used in track seek, the jerk has a maximum value at the start and end of track see, as indicated in Equation 3.
                                                                                                                      j                    ⁡                                          (                      t                      )                                                        =                                                            K                      A                                        ⁢                                          I                      M                                        ⁢                                                                  2                        ⁢                                                                                                  ⁢                        π                                                                    T                        sK                                                              ⁢                                          cos                      ⁡                                              (                                                                              2                            ⁢                                                                                                                  ⁢                            π                                                                                T                            sK                                                                          )                                                                                                                                                                                                                                j                      ⁡                                              (                        0                        )                                                                                                  =                                                                                                          j                        ⁡                                                  (                                                      T                            sK                                                    )                                                                                                            =                                                                  K                        A                                            ⁢                                              I                        M                                            ⁢                                                                                          ⁢                                                                        2                          ⁢                          π                                                                          T                          sK                                                                                                                                                                              (            3            )                              
Therefore, seek servo control adopting the sine wave acceleration trajectory according to Equation 1 is improved in terms of the jerk when compared with seek servo control using the square wave acceleration trajectory. However, the seek servo using the sine wave acceleration trajectory causes a jerk equal to the maximum value of the sine waves at the start and end of track seek as indicated in Equation 3, which still results in mechanical noise and vibration.
Japanese Publication Patent No. 2001-325006 discloses a positioning device to reduce noise in positioning operations. The positioning device further reduces mechanical noise in a seek mode. This technique is characterized in that vibration and noise are reduced in track seeking by low pass filtering the acceleration trajectory, the velocity trajectory, and the position trajectory. However, since the LPF is additionally needed, the number of circuit elements increases. Moreover, since the jerk is not reduced to zero at the start and end of track seeking, the technique still results in mechanical noise and vibration.